Factor VIIa is a plasma serine protease involved in the initiation of the coagulation cascade. It is present in human blood at a concentration of approximately 500 ng/mL, with about 1% of the total amount in the proteolytically active form factor VIIa (Morrissey, J. H. et al. Blood 1993, 81, 734-744). Factor VIIa binds with high affinity to its cofactor, tissue factor, in the presence of calcium ions to form a complex with enhanced proteolytic activity (Carson, S. D. and Brozna, J. P. Blood Coag. Fibrinol. 1993, 4, 281-292). Tissue factor is normally expressed in cells surrounding the vasculature and within the vessel wall, and is exposed to factor VIIa in blood by vessel injury or atherosclerotic plaque rupture. Once formed, the tissue factor/factor VIIa complex initiates blood coagulation by proteolytic cleavage of factor X to factor Xa, factor IX to factor IXa and autoactivation of additional factor VII to VIIa. Factor Xa, generated either directly by tissue factor/factor VIIa or indirectly through action of factor IXa, catalyzes the conversion of prothrombin to thrombin. Thrombin coverts fibrinogen to fibrin, which polymerizes to form the structural framework of a blood clot, and activates platelets, which are a key cellular component of coagulation (Hoffman, M. Blood Reviews 2003, 17, S1-S5). In addition, there is evidence that tissue factor is present in blood, likely in an encrypted form that is de-encrypted during clot formation. (Giesen, P. L. A. et al. Proc. Natl. Acad. Sci. 1999, 96, 2311-2315; Himber, J. et al. J. Thromb. Haemost. 2003, 1, 889-895). The tissue factor/factor VIIa complex derived from blood borne tissue factor may play an important role in propagation of the coagulation cascade (clot growth) and in thrombus formation in the absence of vessel wall injury (i.e., stasis induced deep vein thrombosis or sepsis). The source of blood borne tissue factor is an area of active research (Morrissey, J. H. J. Thromb. Haemost. 2003, 1, 878-880).
While blood coagulation is essential to the regulation of an organism's hemostasis, it is also involved in many pathological conditions. In thrombosis, a blood clot, or thrombus, may form and obstruct circulation locally, causing ischemia and organ damage. Alternatively, in a process known as embolism, the clot may dislodge and subsequently become trapped in a distal vessel, where it again causes ischemia and organ damage. Diseases arising from pathological thrombus formation are collectively referred to as thrombotic or thromboembolic disorders and include acute coronary syndrome, unstable angina, myocardial infarction, ischemic stroke, deep vein thrombosis, peripheral occlusive arterial disease, transient ischemic attack, and pulmonary embolism. In addition, thrombosis occurs on artificial surfaces in contact with blood, including catheters and artificial heart valves. Therefore, drugs that inhibit blood coagulation, or anticoagulants, are “pivotal agents for prevention and treatment of thromboembolic disorders” (Hirsch, J. et al. Blood 2005, 105, 453-463).
Because of its key role in the coagulation cascade, researchers have postulated that inhibition of factor VIIa could be used to treat or prevent thrombotic or thromboembolic disease. (Girard, T. J.; Nicholson, N. S. Curr. Opin. Pharmacol. 2001, 1, 159-163; Lazarus, R. A., et al. Curr. Med. Chem. 2004, 11, 2275-2290; Frederick, R. et al. Curr. Med. Chem. 2005, 12, 397-417.) Several studies have confirmed that various biological and small molecule inhibitors of factor VIIa have in vivo antithrombotic efficacy with a low bleeding liability. For instance, it has been demonstrated that a biological factor VIIa inhibitor XK1, comprising a hybrid of Factor X light chain and tissue factor pathway inhibitor first kunitz domain, prevents thrombus formation in a rat model of arterial thrombosis, with no change in bleeding time or total blood loss (Szalony, J. A. et al. J. Thrombosis and Thrombolysis 2002, 14, 113-121). In addition, small molecule active site directed factor VIIa inhibitors have demonstrated antithrombotic efficacy in animal models of arterial thrombosis (Suleymanov, O., et al. J Pharmacology and Experimental Therapeutics 2003, 306, 1115-1121; Young, W. B., et al. Bioorg. Med. Chem. Lett. 2006, 16, 2037-2041) and venous thrombosis (Szalony, J. A., et al. Thrombosis Research 2003, 112, 167-174; Arnold, C. S., et al. Thrombosis Research 2006, 117, 343-349), with little impact on bleeding time or blood loss. Moreover, the biological factor VIIa inhibitor recombinant nematode anticoagulant protein c2 (rNAPc2) is currently under clinical investigation for treatment of acute coronary syndromes. Results of initial clinical trials demonstrate that rNAPc2 reduces systemic thrombin generation in patients undergoing coronary angioplasty (Moons, A. H. M. J. Am. Coll. Cardiol. 2003, 41, 2147-2153) and that it prevents deep vein thrombosis in patients undergoing total knee replacement (Lee, A., et al. Circulation 2001, 104, 74-78).
Work has accordingly been performed to identify and optimize factor VIIa inhibitors. For example, U.S. Pat. No. 5,866,542 describes recombinant nematode anticoagulant proteins which inhibit factor VIIa. U.S. Pat. No. 5,843,442 discloses monoclonal antibodies or antibody fragments possessing factor VIIa inhibitory activity, and U.S. Pat. No. 5,023,236 presents tripeptides and tripeptide derivatives that inhibit factor VIIa.
An alternative way of initiation of coagulation is operative when blood is exposed to artificial surfaces (e.g., during hemodialysis, ‘on-pump’ cardiovascular surgery, vessel grafts, bacterial sepsis). This process is also termed contact activation. Surface absorption of factor XII leads to a conformational change in the factor XII molecule, thereby facilitating activation to proteolytically active factor XII (factor XIIa and factor XIIf). Factor XIIa (or XIIf) has a number of target proteins, including plasma prekallikrein and factor XI. Active plasma kallikrein further activates factor XII, leading to an amplification of contact activation. Activated FXI acts on FIX, which acts through the coagulation cascade to produce thrombin. Thus, inhibitors of plasma kallikrein would be expected to exert an antithrombotic effect under conditions of contact activation. Contact activation is a surface mediated process responsible in part for the regulation of thrombosis and inflammation, and is mediated, at least in part, by fibrinolytic-, complement-, kininogen/kinin-, and other humoral and cellular pathways (for review, Coleman, R. Contact Activation Pathway, pages 103-122 in Hemostasis and Thrombosis, Lippincott Williams & Wilkins 2001; Schmaier A. H. Contact Activation, pages 105-128 in Thrombosis and Hemorrhage, 1998).
Plasma kallikrein is a zymogen of a trypsin-like serine protease and is present in plasma at 35 to 50 μg/mL. The gene structure is similar to that of factor XI; overall, the amino acid sequence of plasma kallikrein has 58% homology to factor XI. Proteolytic activation by factor XIIa at an internal 1389-R390 bond yields a heavy chain (371 amino acids) and a light chain (248 amino acids). The active site of kallikrein is contained in the light chain. The light chain of plasma kallikrein reacts with protease inhibitors, including alpha 2 macroglobulin and C1-inhibitor. Interestingly, heparin significantly accelerates the inhibition of plasma kallikrein by antithrombin III in the presence of high molecular weight kininogen (HMWK). In blood, the majority of plasma kallikrein circulates in complex with HMWK. Kallikrein cleaves HMWK to liberate bradykinin. Bradykinin release results in increase of vascular permeability and vasodilation (for review, Coleman, R. Contact Activation Pathway, pages 103-122 in Hemostasis and Thrombosis, Lippincott Williams & Wilkins 2001; Schmaier A. H. Contact Activation, pages 105-128 in Thrombosis and Hemorrhage, 1998). Inhibitors of plasma kallikrein would be expected to reduce potential for bradykinin release and thus to exert an anti-inflammatory effect.
While a number of factor VIIa inhibitors have been discussed in the art, improved inhibitors, especially non-peptide inhibitors, of serine proteases for the treatment of thromboembolic disorders are always desirable. The present invention discloses phenylglycinamide and pyridylglycinamide derivatives and analogues thereof, as inhibitors of coagulation Factor VIIa and, as such, their utility in the treatment of thromboembolic disorders.
In addition, it is also desirable to find new compounds with improved pharmacological characteristics compared with known serine protease inhibitors. For example, it is preferred to find new compounds with improved factor VIIa inhibitory activity and selectivity for factor VIIa versus other serine proteases. Also, it is preferred to find new compounds with improved plasma kallikrein inhibitory activity and selectivity for plasma kallikrein versus other serine proteases. Also, it is preferred to find new compounds with improved activity in in vitro clotting assays, such as the prothrombin time (PT) assay or activated partial thromboplastin time assay (APTT) (for a description of the PT and APTT assays see, Goodnight, S. H.; Hathaway, W. E. Screening Tests of Hemostasis. Disorders of Thrombosis and Hemostasis: a clinical guide, 2nd edition, McGraw-Hill: New York, 2001 pp. 41-51). It is also desirable and preferable to find compounds with advantageous and improved characteristics in one or more of the following categories, which are given as examples and are not intended to be limiting: (a) pharmacokinetic properties, including oral bioavailability; (b) pharmaceutical properties; (c) dosage requirements; (d) factors which decrease blood concentration peak-to-trough characteristics; (e) factors that increase the concentration of active drug at the receptor; (f) factors that decrease the liability for clinical drug-drug interactions; (g) factors that decrease the potential for adverse side-effects; and, (h) factors that improve manufacturing costs or feasibility.